A known valve timing control apparatus of this kind includes a driving side rotational member, which rotates synchronously to a crankshaft, and a driven side rotational member which is arranged coaxially to the driving side rotational member so as to rotate relative to the driving side rotational member and to rotate integrally to a camshaft. According to the known valve timing control apparatus, a fluid pressure chamber is formed between the driving side rotational member and the driven side rotational member. The fluid pressure chamber is defined into an advanced angle chamber and a retarded angle chamber. The known valve timing control apparatus further includes a relative rotational phase adjusting mechanism which is capable of adjusting a relative rotational phase of the driving side rotational member and the driven side rotational member between a most advanced angle phase where the volume of the advanced angle chamber is maximized and a most retarded angle phase where the volume of the advanced angle chamber is minimized by supplying or draining a working fluid to or from the advanced angle chamber and the retarded angle chamber.
With an engine which includes the known valve timing control apparatus explained above, upon the rotation of the crankshaft, the rotation of the crankshaft is transmitted to the driving side rotational member via a chain belt or a timing belt to rotate the camshaft connected to the driving side rotation member. Accordingly, the camshaft rotates with a constant ratio of rotation speed relative to a rotation speed of the crankshaft (that is, engine rotation speed).
Upon the rotation of the camshaft, the intake valves and/or the exhaust valves (i.e., hereinafter referred to as the valve) are operated in response to the operation of cams. In those circumstances, the camshaft receives a fluctuated torque every time the valve operates. In other words, the camshaft receives a torque applied in a reverse direction reversing from the rotating direction by a resistance force caused by a compression of a valve spring when opening the valve (i.e., reversing torque), and receives a torque in the same direction to the rotating direction by a biasing force deriving from the extension of the valve spring when closing the valve (i.e., positive torque). The torque fluctuation in the positive and reverse directions which is received by the camshaft affects the driven side rotational member.
Normally, relative rotational phase of the driven side rotational member relative to the driving side rotational member is positioned at the most retarded angle phase before the engine starting. Upon the starting of the engine, the working fluid is supplied to an advanced angle oil path by the relative rotational phase adjusting mechanism. When a lock pin is released by the hydraulic pressure of the working fluid, the working fluid is supplied to the advanced angle chamber to displace the driven side rotational member in an advancing direction.
However, at the engine start-up, because the hydraulic pressure in the engine is not adequately enhanced and the fluid pressure chamber is not filled with working fluid, the driven side rotational member is susceptible to the fluctuated torque by the operation of the cam. Namely, the driven side rotational member is gradually displaced in the advancing direction accompanying undesired fluctuated movement by alternately receiving the fluctuated torque in the positive direction and in the reverse direction. In those circumstances, in case the fluctuated torque in the positive direction exceeds the torque applied to the driven side rotational member by the relative rotational phase adjusting mechanism to excessively advance the driven side rotational member in the advancing angle direction, the inside of the advanced angle chamber has a vacuum pressure instantly. This hampers the displacement of the driven side rotational member in the advancing angle direction. As a result, the undesired fluctuated movement of the driven side rotational member can be restrained to some extent.
On the other hand, immediately after the engine start-up, it is required to quickly set the relative rotational phase of the driving side rotational member and the driven side rotational member to be a predetermined state. A known valve timing control apparatus described in JP2002-168103A attempts to quickly displace the driven side rotational member in the advancing angle direction effectively using the undesired fluctuated movement of the driven side rotational member in the advancing angle direction when receiving the fluctuated toque.
According to the valve timing control apparatus described in JP2002-168103A, a communication passage which communicates the advanced angle chamber and the retarded angle chamber is formed on the driving side rotational member. A control valve, which allows the working fluid to flow from the retarded angle chamber to the advanced angle chamber and which impedes a flow of the working fluid from the advanced angle chamber to the retarded angle chamber, is provided at the communication passage. When the camshaft further rotates in the advancing angle direction receiving the positive torque, in a state where the engine rotation speed is low, for example, at the engine start-up, the control valve functions to move the working fluid in the retarded angle chamber to the advanced angle chamber by a volume corresponding to the degree of the advancing angle. The valve timing control apparatus described in JP2002-168103A assists the advancing movement of the driven side rotational member using vibrations applied in the advancing angle direction out of the vibrations of the driven side rotational member deriving from the torque fluctuation in the positive and reverse directions which is applied to the camshaft.
Notwithstanding, according to the valve timing control apparatus described in JP2002-168103A, because the working fluid passes through the communication passage and the control valve, relatively large flow resistance by the working fluid is generated at the communication passage. Accordingly, a relatively long time is required to move the working fluid from the retarded angle chamber to the advanced angle chamber, and thus the working fluid cannot be quickly supplied to the advanced angle chamber in response to the pressure decrease in the advanced angle chamber. In consequence, immediately after the engine start-up, relatively long time is required before the driven side rotational member is displaced to be positioned at a predetermined relative rotational phase. Further, because the communication passage and the control valve are formed inside the driving side rotational member, rotation of the driving side rotational member is unbalanced and the structure thereof is also complicated. Still further, because an operational direction of a movable member, which is provided at the control valve, is directed approximately along the rotational direction of the driving side rotational member, an accelerating force or a decelerating force is applied to the movable member in accordance with changes of the rotational speed of the driving side rotational member, which is likely to bring the erroneous operation of the control valve.
A need thus exists for a valve timing control apparatus, which is not susceptible to the drawback mentioned above.